JP4340355B2 - Wavelength gain characteristic shift filter, optical transmission apparatus and optical transmission method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical transmission device, and more particularly to a wavelength gain characteristic shift filter, an optical transmission device, and an optical transmission method suitable for wavelength division multiplexing transmission.
[0002]
[Prior art]
In order to cope with the rapid increase in traffic accompanying the rapid spread of the Internet, dense wavelength division multiplexing (DWDM) is being realized in North America. This DWDM is realized because the optical amplifier used for collective amplification of wavelength multiplexed light has an amplification band. However, the gain of the optical amplifier has wavelength dependency, and the wavelength dependency also changes depending on the input level. For this reason, the current wavelength division multiplexing transmission cannot use the entire amplification band of the optical amplifier, and only uses a band called a red band whose wavelength dependency of gain is relatively flat.
[0003]
As publicly known examples related to the present invention, there are JP-A Nos. 08-278523 and 11-150526.
[0004]
[Problems to be solved by the invention]
The present invention dynamically adjusts the gain according to the input level. Price An object of the present invention is to realize a wavelength gain characteristic shift filter. Another object of the present invention is to provide an optical transmission apparatus suitable for wavelength division multiplexing transmission. Another object of the present invention is to provide an optical transmission method suitable for wavelength division multiplexing transmission.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a wavelength gain characteristic comprising a filter unit obtained by changing a temperature of a filter characteristic corresponding to a wavelength gain characteristic for a plurality of input levels of an optical amplifier, and a Peltier element for controlling the temperature of the filter unit This is achieved by using a shift filter. In addition, this is achieved by providing an optical transmission apparatus including a wavelength gain characteristic shift filter that compensates for a wavelength gain characteristic according to an input level, an optical gain adjuster, and an optical amplifier that amplifies optical signals having a plurality of wavelengths. . Furthermore, this is achieved by providing an optical transmission device characterized in that the amplification band is divided at least at a wavelength that gives an inflection point of the wavelength gain characteristic of the doped fiber and the gain is adjusted for each divided wavelength band.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram of an example of an optical transmission apparatus according to an embodiment of the present invention. In this embodiment, the signal light wavelength bands supplied from the optical transmitter 1 are λ1 = 13531 ± 1.5 nm, λ2 = 1534 ± 1.5 nm, λ3 = 1537 ± 1.5 nm, and λ4 = 1549.5 ± 11 nm. Λ5 = 1510 ± 10 nm. λ5 is a wavelength band of monitoring light standardized by ITU-T, and λ1 to λ4 are wavelength bands of signal light. Here, the boundary between the wavelength band of the signal light and the wavelength band is a wavelength that gives an inflection point of the wavelength-gain characteristic of an erbium-doped fiber (EDF) of the optical amplifier. The reason for this will be described later. λ1 to λ5 are divisions for convenience in explaining the effects of the invention, and each wavelength band does not necessarily follow this division, and may be further subdivided. Any number of signal wavelengths may be multiplexed in each band. Further, a band centered at 1480 nm may be used as λ5.
[0007]
The input signal light Pin multiplexed with λ1 to λ5 passes through the optical connector 60 that separates the actual line and the transmission device, and is demultiplexed into λ1 to λ4 and λ5 by the first monitoring light multiplexer / demultiplexer 61. The demultiplexed λ5 is delivered to the first line monitoring device 62. On the other hand, λ1 to λ4 are input to the first optical amplifying device 64 via the first optical splitter 63. The light partially branched by the first optical branching device 63 is detected by the first optical receiver 65 and sends a first optical monitor signal to the first control device 66.
[0008]
The light amplified by the first optical amplifying device 64 is partially branched by the second optical splitter 67 and then input to the first optical demultiplexer 68. The branched light is detected by the second optical receiver 69, and a second optical monitor signal is sent to the first controller 66. The first optical demultiplexing device 68 is an optical demultiplexing device for demultiplexing λ1 to λ3 and λ4, where λ1 to λ3 are in the first demultiplexing path and λ4 is the second demultiplexing. Demultiplexed into the path.
[0009]
Here, the details of the first optical demultiplexing device 68 will be described with reference to FIG.
FIG. 2 is a block diagram of the optical demultiplexing device 68. In the optical demultiplexing device 68, the input signal lights λ 1 to λ 4 are first input to the optical isolator 70. The light that has passed through the optical isolator 70 is branched into two paths by the optical splitter 71. On each path, it is introduced into optical notch filters 74 and 75 for removing light components that are adjacent to the passband and cannot be removed only by the optical filters 72 and 73.
[0010]
The signal light that has passed through the optical notch filters 74 and 75 is further shielded from out-of-band signal light by the optical filters 72 and 73. In this configuration, as the optical notch filters 74 and 75, fiber grating type optical notch filters that effectively shield the signal light located in the grid next to the in-band signal light are applied. At the same time, when the fiber grating type optical notch filters 74 and 75 are used at the same time, the reflected light returns in the reverse direction of the signal light. Therefore, in order to prevent this, the optical isolator 70 is used in combination with the preceding stage of the optical splitter 71. It was.
[0011]
The reason for using the optical notch filters 74 and 75 that shield the signal light located in the grid next to the signal light in the passband is that noise light outside the passband that has the most adverse effect on the passband This is because it is important to remove the signal light.
[0012]
More effectively, it is desirable to connect in series an optical notch filter with a wide band that removes a plurality of adjacent signal lights, or an optical notch filter that shields each of the plurality of signal lights independently.
[0013]
With the optical multiplexing device of this embodiment, it becomes possible to separate the crosstalk in and out of the band to 30 dB or more. Further, the optical demultiplexing device 68 of this configuration has an effect that the wavelength band of the optical amplifier can be effectively used in that the band can be divided continuously without skipping the wavelength grid. Thereby, the cost per wavelength of the optical transmission system can be reduced, and the cost merit can be increased.
[0014]
Returning to FIG. 1, the amplification process of λ1, λ2, and λ3 following the first path will be described. In the optical transmission apparatus of this embodiment, each wavelength band can be adjusted independently for each wavelength band. Utilizing this feature, optical connectors 76 and 91 are provided on the first path in order to make it possible to separate the adjustment amplification function of the wavelength band of λ1 to λ3.
[0015]
The signal light of λ1 to λ3 that has passed through the optical connector 76 is partly branched by the third optical splitter 77 and then input to the second optical demultiplexer 78. The branched light is detected by the third light receiver 79. With this configuration, the attachment / detachment of the optical connector 76 can be monitored.
[0016]
The second optical demultiplexer 78 is an optical demultiplexer for demultiplexing λ1, λ2, and λ3, where λ1 is a third demultiplexing path and λ2 is a fourth demultiplexer. To the path, λ3 is demultiplexed to the fifth demultiplexing path. The configuration of the optical demultiplexer 78 is the same as that of the optical demultiplexer 68, and the optical branching device 71 is simply changed into three branches. The demultiplexed λ1 is introduced into the first optical gain adjusting device 80, adjusted to a predetermined gain, and then introduced into the third optical multiplexer 81. The configuration of the optical multiplexer is the same as that of the optical demultiplexer 78, except that the input and output are opposite to each other and the optical isolator is omitted. Similarly, λ 2 and λ 3 are introduced into the second and third optical gain adjusting devices 82 and 83, adjusted to a predetermined gain, and then introduced into the third optical multiplexer 81.
[0017]
The combined signal light of λ1 to λ3 is shielded from the influence of the reflected light from the latter-stage optical component, and passes through the optical isolator 84 that simultaneously exhibits the effect on the signal light of λ1 to λ3 to the dispersion compensator 85. be introduced. The dispersion compensator 85 has a characteristic opposite to the dispersion characteristic inherent to the line optical fiber, and may be removed if unnecessary depending on the type of the line optical fiber. An optical connector may be provided at both ends of the dispersion compensator 85 so as to be separable. This makes it possible to replace and insert an appropriate dispersion compensator for the line. Even in this case, the effect of the present invention is not lost.
[0018]
The signal light from the dispersion compensator 85 is partially branched by the fourth optical splitter 86 and then amplified by the second optical amplifier 87. The branched light is detected by the fourth optical receiver 88 and sends a third optical monitor signal to the second controller 89. On the other hand, the amplified signal light is partly branched by the fifth optical splitter 90, passes through the optical connector 91, and is introduced into the fourth optical multiplexer 92. The branched light is detected by the fifth optical receiver 93, and a fourth optical monitor signal is sent to the second control device 89.
[0019]
Next, the amplification process of λ4 that follows the second path will be described.
The signal light of λ4 is introduced into the fourth optical gain adjusting device 94, adjusted to a predetermined gain, and then passed through the optical isolator 95 and introduced into the second dispersion compensator 96. The signal light from the second dispersion compensator 96 is partially branched by the sixth optical splitter 97 and then amplified by the third optical amplifier 98. The branched light is detected by the sixth optical receiver 99 and sends a fifth optical monitor signal to the third control device 100. On the other hand, the amplified signal light is partly branched by the seventh optical splitter 101 and then introduced into the fourth optical multiplexer 92. The branched light is detected by the seventh optical receiver 102 and sends a sixth optical monitor signal to the third control device 100.
[0020]
The optical signals of λ1 to λ3 are combined with the optical signal of λ4 amplified by the fourth optical multiplexer 92, and λ1 to λ4 and the second line monitoring device 104 are combined by the second monitoring optical optical multiplexer 103. The monitoring light λ5 is combined and output to the line via the optical connector 151.
Optical connectors may be provided at both ends of the second dispersion compensator 96 so as to be separable. As a result, it is possible to replace and insert a dispersion compensator having appropriate characteristics in the line.
[0021]
As already described, in this embodiment, since independent adjustment is possible for each wavelength band, a configuration is adopted in which amplification transmission is performed from the initial stage where λ4 is installed as a transmission device. As a desirable application method, a signal light having a wavelength band of λ4 and a monitoring light having a wavelength of λ5 are transmitted as a first stage of installation, and a signal light having a wavelength band of λ1 to λ3 is transmitted as a second stage which is an expansion stage. Is preferred.
[0022]
This is because the optical amplifying apparatus is designed to support the maximum number of wavelength multiplexing, but is often operated with a small number of wavelength multiplexing at the initial stage of installation of the transmission system. This is because the tightness of the line and the increase in the transmission capacity are not temporarily done but often increase gradually. Since the transmission apparatus according to the present embodiment can be independently adjusted for each wavelength band, an optical transmission system that can cope with future increase in transmission capacity with less initial investment can be obtained.
[0023]
At the same time, the fact that it can be adjusted independently means that it does not affect the facilities already in operation at the time of expansion, which has a great merit.
Further, depending on the application, there may be a case in which the signal light in the wavelength band of λ1 to λ3 and the monitoring light of λ5 are transmitted as the first stage and λ4 is transmitted as the second stage. In that case, an optical connector may be provided on the second path between the first optical multiplexer 68 and the fourth optical gain adjusting device 94 and in front of the fourth optical multiplexer 92 so as to be separable. good.
[0024]
Next, the function of the optical gain adjusting apparatus according to another embodiment of the present invention will be described in detail with reference to FIG. In FIG. 1, the optical gain adjusting device is indicated by reference numerals 80, 81, 83 and 94. Although the description here is for the optical gain adjusting device 94, the other optical gain adjusting devices 80, 82, and 83 operate in the same manner. The optical gain adjusting device 94 includes an optical gain adjuster 105, a wavelength gain characteristic shift filter 109, an optical splitter 113, an optical receiver 121 that receives light branched from the optical splitter 113, and an optical receiver 121. The control device 129 controls the optical gain adjuster 105 based on the monitor information from, and the wavelength gain characteristic shift filter control devices 133, 134, 135, 136 control the wavelength gain characteristic shift filter 109.
[0025]
Among the components inside the optical amplifying device, the fixed gain characteristic caused by the passive component is not a relatively large problem. In actual use, the most important and significant problem is that the gain characteristics of the optical amplifying medium in the optical amplifying apparatus vary greatly depending on the input power input to the transmission apparatus. In general, it is known that an optical amplifier varies in gain deviation depending on signal gain.
[0026]
On the other hand, it is required to keep the output level of the transmission device within a certain range because of the line design requirement to prevent the non-linear effect of the transmission fiber and to enable longer distance transmission. Therefore, the required gain of the optical amplifying device changes as the input power changes, and as a result, the gain characteristics vary greatly.
[0027]
In this embodiment, the optical gain adjuster 105 can independently adjust the gain deviation between wavelengths generated by the first optical amplifier 64 and the third optical amplifier 98. This optical gain adjuster will be described with reference to FIG. FIG. 3 is a block diagram illustrating the configuration of the optical gain adjuster. The optical gain adjuster 105 includes an EDF 301, a pumping light source 302, and an optical multiplexer 303. In this embodiment, a light emitting diode having a wavelength of 820 nm is used as an excitation light source. However, a wavelength of 1480 nm or 980 nm or a laser diode may be used.
[0028]
When the excitation light source 302 is highly excited, the excitation light from the excitation light source 302 enters from the rear end of the EDF 301 by the optical multiplexer 303 and excites the EDF 301. The signal light in the wavelength band of λ4 enters from the front end of the EDF 301, and is output after being amplified. On the other hand, when the excitation light source 302 is low excitation or does not emit light, the EDF 301 attenuates the signal light. That is, the optical gain adjuster 105 functions as an optical gain adjuster having a positive or negative gain by adjusting the pump current of the pump light source 302.
[0029]
Here, since the EDF 301 does not require excessive amplification characteristics, it may be about 3 m. Further, the output of the 830 nm wavelength light emitting diode used for the excitation light source 302 may be about 20 mW.
[0030]
The wavelength gain characteristic shift filter of the present embodiment complements its function in combination with the optical gain adjuster, and greatly enhances its effect. That is, first, the generated gain deviation is corrected by the optical gain adjuster independently for each wavelength band. Furthermore, the gain deviation that cannot be corrected by the optical gain adjuster is corrected by the wavelength gain characteristic shift filter.
[0031]
The configuration of the optical gain auxiliary adjuster will be described with reference to FIG. Here, FIG. 4 is a block diagram of the wavelength gain characteristic shift filter.
Hereinafter, the wavelength band of λ2 will be described as an example, but the same applies to other wavelength bands.
The wavelength gain characteristic shift filter 111 according to the present embodiment includes a temperature-dependent optical filter 138, a Peltier element 139 as a temperature controller, and a thermistor resistor 140 for detecting the temperature of the optical filter 138. Yes. Here, as the optical filter 138, an etalon filter or a fiber grating filter can be applied. However, other types of filters may be used as long as they do not depart from the spirit of the present invention. A fiber grating type filter called Long Period Grating, which is a highly dependent device, was applied.
[0032]
Next, the design of the filter characteristics of the fiber grating type filter will be specifically described with reference to FIGS. Here, FIG. 5 is a wavelength-gain curve diagram of the EDF obtained using the input level as a parameter, FIG. 6 is a diagram in which the four wavelength-gain curves of FIG. 5 are continuously arranged, and FIG. It is the figure calculated | required as a filter characteristic.
[0033]
FIG. 5 is a curve plotting the relationship between the wavelength and gain of the EDF in the region of λ 2 with the input level as a parameter. Here, a gain curve of 36 dB at 1532.5 nm has the lowest input level, and a gain curve of 26 dB at the same wavelength has the highest input level. As is apparent from the figure, in this wavelength region, the gain characteristics change greatly due to changes in the input level to the EDF.
[0034]
FIG. 6 is a curve in which the four wavelength-gain curves shown in FIG. 5 are shifted little by little in the direction of the wavelength axis while maintaining their respective shapes, and approximate curves asymptotically approaching all points are drawn. The meaning of FIG. 6 is that a curve indicating a change in gain characteristic occurring in the same λ2 wavelength band is reproduced by a continuous change (shift) in the wavelength axis direction.
[0035]
Next, FIG. 7 is a graph showing the insertion loss characteristic of the optical filter 138 having the opposite characteristic to that of FIG. In this embodiment, the design can be made with a reproduction accuracy of 0.1 dB. Although the wavelength band of λ2 is originally 3 nm, the optical filter 138 has loss characteristics corresponding to all the input levels shown in FIG. 5 in the 7 nm band.
[0036]
The temperature characteristic of the fiber grating filter of this example is 0.08 nm / ° C., and a wavelength shift of 4 nm is possible by changing a temperature change of about 50 ° C. by a Peltier element. Specifically, assuming that the center of the temperature variable region is 25 ° C., the center of the 7 nm band of the optical filter 138 is made to coincide with the center wavelength of λ 2 at 25 ° C. Thereby, the loss characteristic of the optical filter can be changed by −2 nm by shifting −25 ° C. to the low temperature side with respect to 25 ° C., and +2 nm by shifting 25 ° C. to the low temperature side.
[0037]
The function as the wavelength gain characteristic shift filter 94 will be described with reference to FIGS. 4, 5, and 7. An optical amplifier that performs constant output amplification when the input level is small gives a large gain to the optical signal, and the gain deviation between wavelengths is large as shown by the uppermost curve in FIG. At this time, the Peltier device 139 in FIG. 4 is controlled to raise the temperature. As a result, the temperature of the optical filter 138 increases. The filter characteristics of the optical filter 138 shift to the high wavelength side in FIG. 7 due to the temperature rise. As a result, the gain-to-wavelength deviation can be compensated.
[0038]
In this embodiment, the temperature characteristic of the filter is 0.08 nm / ° C., but it goes without saying that the temperature change range can be narrowed by applying a device having a higher temperature dependency. On the other hand, if it is 0.01 nm / ° C. or higher, a 0.5 nm shift is possible in the temperature range of 0 to 50 ° C., so that the effect of the invention can be sufficiently obtained depending on the applied wavelength band.
[0039]
On the other hand, the unit of nm / ° C. is a notation for expressing the characteristics approximately in an easy-to-understand manner, and may be negative characteristics or the characteristics may differ depending on the temperature region. For example, the device may be +0.01 nm / ° C., −0.01 nm / ° C., 0.03 nm / ° C. at 0-20 ° C., or 0.09 nm / ° C. at 20-50 ° C.
[0040]
Here, it will be explained that it is important to place the boundary of the wavelength band described at the beginning of the embodiment. In order to realize an appropriate loss characteristic of the wavelength gain characteristic shift filter continuously and with a very small error only by shifting the wavelength, it is necessary to prevent the inflection point from being included in the gain characteristic of the wavelength band. Therefore, in the present invention, the boundary between the wavelength band of the signal light and the wavelength band is a wavelength that provides a turning point of the wavelength-gain characteristic of the EDF of the optical amplifier. However, as described above, it may be further finely divided. By finely dividing the filter, the filter characteristics can be controlled in a narrow temperature variable region.
[0041]
Further, as a method for more effectively controlling, a method of connecting the wavelength gain characteristic shift filters in a column can be considered. For example, if the preceding wavelength gain characteristic shift filter and the latter wavelength gain characteristic shift filter are controlled with different wavelength characteristics, more complicated wavelength characteristics can be realized.
[0042]
Next, as means for realizing the present invention, a method of actually controlling the optical gain adjuster and the wavelength gain characteristic shift filter will be described with reference back to FIG.
First, in the optical amplifying apparatus according to the present embodiment, the purpose is to perform control in which the optical output per signal that is finally output to the line is constant without depending on the input level to the optical amplifying apparatus. .
[0043]
In addition, the dispersion compensator has an input power limit. When light of a predetermined level or higher is introduced, a phenomenon that the signal waveform is distorted due to the nonlinear effect of light is observed. In this embodiment, in order to avoid this phenomenon, the signal input level of the dispersion compensator is controlled to be +0 dBm or less for each signal.
[0044]
First, the first optical amplifier 64 can obtain the amplification gain by monitoring the input level and the output level, and is controlled by the first controller 66 so as to adjust the gain according to the input level. For example, when the input level is -30 dBm, which is the lowest, the gain is controlled to be about 30 dB. When the input level is +5 dBm, the gain is controlled to be about 5 dB.
[0045]
Next, the optical gain adjusters 105, 106, 107, 108 monitor the optical output level and control it to a constant output so that each signal wavelength becomes +0 dBm or less. At this time, the gains of the optical gain adjusters 105, 106, 107, and 108 are determined to predetermined values. The determined gain can be monitored for amplification or attenuation gain from input monitoring to the optical gain adjusters 105, 106, 107, 108.
[0046]
Next, the signal light passing through this path passes through the dispersion compensator 85 and is amplified by the second optical amplifying device 87. The second optical amplifying device 87 controls the line light output to be constant at +8 dBm for each signal wavelength. The gain of the second optical amplifier 87 is determined by the loss amount of the dispersion compensator 85. The gain thus determined can be monitored from the input monitor to the second optical amplifying device 87.
[0047]
In this way, the gain from the input to the output to the optical amplifying device is determined for each path, and the gain information is collected in the wavelength gain characteristic shift filter control devices 133, 134, 135 and 136.
[0048]
For example, assuming that the gain of the first optical amplifier 64 is 25 dB, the gain of the optical gain adjusters 105, 106, 107, and 108 is 10 dB, and the gain of the second optical amplifier 87 is 18 dB, the gain information is the wavelength. The gain characteristic shift filter control devices 133, 134, 135, and 136 are summarized.
[0049]
As described above, the gain deviation changes depending on the gain by the optical amplifier. The amount of adjustment of the wavelength gain characteristic shift filter 109, 110, 111, 112 with respect to the gain is set in advance, and the wavelength gain characteristic shift filter controller 133, 134, 135, so as to perform predetermined adjustment from the detected gain information. The wavelength gain characteristic shift filters 109, 110, 111 and 112 are controlled by 136.
Similar control is performed for the fourth route.
[0050]
With reference to FIG. 8, another embodiment of the present invention for controlling the optical gain auxiliary adjustment devices 109, 110, 111, 112 in a manner different from the embodiment of FIG. 1 will be described. Here, FIG. 8 is a block diagram of an optical transmission apparatus according to an embodiment of the present invention.
[0051]
The control method of each optical amplifier and each optical gain adjuster is the same as that of the embodiment of the optical transmission apparatus shown in FIG. The wavelength multiplexed output output from the optical amplifying device is introduced into the optical demultiplexing devices 137-1 and 137-2, and is demultiplexed for each wavelength. The demultiplexed wavelengths are partly branched by the optical splitters 138-1 to 138-n, and monitored by the optical receivers 139-1 to 139-n for each wavelength. In this configuration, the wavelength gain characteristic shift filters 109, 110, 111, and 112 are controlled so that the light level of each wavelength becomes a predetermined value.
[0052]
With this configuration, the wavelength characteristics can be directly monitored, and the control accuracy is improved. Further, since the optical power auxiliary adjuster can be controlled without necessarily depending on the gain of the optical amplifier in the optical amplifying device, the degree of freedom in control during actual use is improved.
[0053]
The optical gain adjusters 140-1 to 140-n and the optical demultiplexers 137-1 and 137-2 are configured by applying the optical power adjuster 8 that adjusts each signal wavelength independently. The light branched by 141-2 to 142-n is monitored by the optical receivers 143-1 to 143-n so that the light is controlled with the control devices 141-1 to 141-n so as to obtain a constant output. ing.
[0054]
The positions of the optical power adjuster 8 and the gain adjuster 94 may be after the optical branching device 90 or the optical branching device 101.
[0055]
An embodiment in which the optical gain auxiliary adjustment devices 109, 110, 111, and 112 are controlled by a method different from that of FIGS. 1 and 8 will be described. Here, FIG. 9 is a block diagram of an optical transmission apparatus according to an embodiment of the present invention.
[0056]
The control method of each optical amplifier and each optical gain adjuster is the same as that shown in FIGS.
The optical gain adjusters 146-1 to 146-n and the optical multiplexers 150-1 and 150-2 apply the optical power adjuster 8 that adjusts each signal wavelength independently. The input light is detected by monitoring the light branched by the optical splitters 144-1 to 144-n by the optical receivers 145-1 to 145-n, while being branched by the optical splitters 148-1 to 148-n. The configuration is such that the light is monitored by the optical receivers 149-1 to 149-n and controlled by the control devices 147-1 to 147-n so as to obtain a constant output.
[0057]
Each signal output is introduced into the optical multiplexers 150-1 and 150-2 and combined. In this configuration, the output light level of each wavelength is monitored, and the wavelength gain characteristic shift filters 109, 110, 111, and 112 are controlled so as to be amplified with a predetermined gain value for these output levels.
The positions of the optical power adjuster 8 and the gain adjuster 94 may be in front of the optical branching device 90 or the optical branching device 101.
[0058]
With this configuration, the amplification gain can be directly managed with respect to the input signal gain, so that the control accuracy is improved. In addition, since the wavelength gain characteristic shift filter can be controlled without necessarily depending on the gain of the optical amplifier in the optical amplifier, the degree of freedom in control during actual use is improved.
[0059]
A feature of each of the embodiments described above is that the gain characteristic of the rare earth-doped optical fiber that is an optical amplifying medium is regarded as a curve having a plurality of inflection points, and wavelength division is performed in the vicinity of the inflection points. The divided wavelength band almost spans between the inflection points. By dividing the structure as described above, it is possible to actually replace a gain deviation that occurs between the same wavelengths with a gain deviation that continuously occurs at different wavelengths. As described in detail, it is impossible to replace the gain regulator that can be independently adjusted for each wavelength band by continuous gain change unless it is divided by the above design method. large.
[0060]
Further, in general, a great improvement effort is put into reducing the temperature dependency of the optical filter. On the other hand, the optical filter included in the auxiliary optical power controller of the present invention is characterized in that a filter having a large temperature characteristic is applied.
[0061]
The function that can be realized by the present invention is to obtain a desired gain characteristic by causing a gain characteristic of a different wavelength band to appear in a desired wavelength band by changing the temperature. In order to easily realize this function, a narrower required temperature variable width is more effective in actual control. For this purpose, an optical filter having a large temperature dependency is required.
[0062]
In addition, the present system, which is realized by simply shifting the gain characteristics that originally exist across different wavelength bands, has a simple configuration and can be easily controlled functionally, and can improve reliability.
However, in the present embodiment, a method of controlling the temperature as a method of obtaining the desired gain characteristic by causing the gain characteristic of the different wavelength band to appear in the desired wavelength band is not necessarily limited to this configuration. . For example, the wavelength characteristic may be changed optically to obtain a desired gain characteristic.
[0063]
In addition, the optical gain adjuster can adjust the optical power in the band and the gain deviation in the band at the same time. Conversely, if the emphasis is on the adjustment of the optical power, the compensation amount of the gain deviation May be insufficient. On the other hand, the wavelength gain characteristic shift filter can adjust the gain deviation, and at the same time, the amount of loss in the band changes, so that the optical power in the band changes. That is, by separately and simultaneously providing the optical gain adjuster and the wavelength gain characteristic shift filter, it is possible to complement the effects of each other and further improve the effects of the conventional invention.
[0064]
By adding a wavelength gain characteristic shift filter to the optical gain adjuster, there is an effect of adjusting the gain deviation generated by the optical amplifier in the apparatus. Furthermore, it becomes possible to sufficiently correct and adjust the integration of gain deviation from the previous stage optical amplifying apparatus, which is a problem when connecting multiple stages of optical amplification apparatuses (even if gain deviation occurs in the previous stage optical amplification apparatus), it becomes possible to It has a significant improvement effect on the transmission system.
[0065]
In the above embodiment, the wavelength gain characteristic shift filter is not specified at the position shown in the figure, and may be installed, for example, at the front stage or the rear stage of the optical gain adjuster.
[0066]
【The invention's effect】
Dynamic gain etc. according to input level Price It was possible to realize a wavelength gain characteristic shift filter. In addition, an optical transmission device capable of efficiently using a wavelength band suitable for wavelength division multiplexing could be provided. Furthermore, an optical transmission method suitable for wavelength division multiplexing could be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram of an optical transmission apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram of an optical demultiplexing device applied to an embodiment of the present invention.
FIG. 3 is a block diagram illustrating a configuration of an optical gain adjuster according to an embodiment of the present invention.
FIG. 4 is a block diagram of a wavelength gain characteristic shift filter according to an embodiment of the present invention.
FIG. 5 is a curve plotting the relationship between the wavelength and gain of an EDF in the region of λ 2 with the input level as a parameter, according to an embodiment of the present invention.
FIG. 6 is a curve depicting approximate curves that gradually shift to the wavelength axis direction by gradually shifting the four wavelength-gain curves of the embodiment of the present invention in the wavelength axis direction while maintaining their respective shapes. .
FIG. 7 is a graph showing insertion loss characteristics of the optical filter 138 according to the embodiment of the present invention.
FIG. 8 is a block diagram of an optical transmission apparatus according to an embodiment of the present invention.
FIG. 9 is a block diagram of an optical transmission apparatus according to an embodiment of the present invention.
[Explanation of symbols]
8 ... Optical power adjuster, 80, 81, 83, 94 ... Optical gain adjuster, 60, 76, 91, 151 ... Optical connector, 61, 68, 78 ... Optical demultiplexer, 62, 104 ... Line monitoring device, 63, 67, 71, 77, 86, 90, 97, 101, 113, 114, 115, 116, 117, 118, 119, 120 ... optical branching device, 64, 98, 87 ... optical amplifier, 65, 69, 79 , 88, 93, 99, 102, 121, 122, 123, 124, 125, 126, 127, 128 ... optical receivers, 66, 89, 100, 129, 130, 131, 132 ... control devices, 105, 106, 107, 108 ... optical gain adjusters, 109, 110, 111, 112 ... wavelength gain characteristic shift filters, 133, 134, 135, 136 ... wavelength gain characteristic shift filter controllers, 70, 4, 95 ... Optical isolator, 81, 92, 103 ... Optical multiplexer, 85, 96 ... Dispersion compensator, 74, 75 ... Optical notch filter, 72, 73 ... Optical filter, 137 ... Wavelength shift filter, 138 ... Fiber grating Type optical filter, 139 ... temperature controller, 140 ... thermistor resistance, 301 ... EDF, 302 ... excitation light source, 303 ... optical multiplexer.

Claims (2)

A wavelength demultiplexing unit that receives optical signals having a plurality of wavelengths and separates them into a plurality of predetermined wavelength bands;
A plurality of filter units that compensate for changes in wavelength gain characteristics that occur depending on an input level for each of optical signals in a plurality of wavelength bands that are output from the wavelength demultiplexing unit;
A plurality of optical gain adjusters for adjusting the gains of the optical signals output from the plurality of filter units;
An optical amplifier that amplifies the optical signal output from the optical gain adjuster,
The optical gain adjuster comprises a rare earth doped optical fiber,
Said wavelength demultiplexing unit, when viewed as a curve having a plurality of inflection points for the wavelength gain characteristic of the optical amplifier, to separate the wavelength band of Oite optical signal to the inflection point,
The filter unit includes a plurality of wavelength gain characteristic shift filters connected in cascade, and compensates for a change in the wavelength gain characteristic so as to equalize the wavelength gain of the optical amplifier. An optical filter whose wavelength gain characteristic changes depending on the Peltier element for controlling the temperature of the optical filter,
The optical filters in each wavelength gain characteristic shift filter have different wavelength gain characteristics, and the Peltier elements in each wavelength gain characteristic shift filter are independently controlled according to the input level of the optical signal. Optical transmission device. A wavelength demultiplexing unit that receives optical signals having a plurality of wavelengths and separates them into a plurality of predetermined wavelength bands;
A plurality of filter units for compensating wavelength gain characteristics for each of optical signals in a plurality of wavelength bands output from the wavelength demultiplexing unit, including a plurality of wavelength gain characteristic shift filters connected in cascade;
A plurality of optical gain adjusters including a first impurity-doped fiber and a first pumping light source and adjusting the gains of the optical signals output from the plurality of filter units;
An optical amplifier including a second impurity-doped fiber and a second pumping light source for amplifying the optical signal output from the optical gain adjuster;
The first impurity-doped fiber is a rare earth-doped optical fiber;
Said wavelength demultiplexing unit, when viewed as a curve having a plurality of inflection points for the wavelength gain characteristic of the optical amplifier, to separate the wavelength band of Oite optical signal to the inflection point,
The filter unit compensates for the change in the wavelength gain characteristic so as to equalize the wavelength gain of the optical amplifier,
Each of the wavelength gain characteristic shift filters includes an optical filter whose wavelength gain characteristic changes depending on temperature, and a Peltier element that controls the temperature of the optical filter, and each of the optical filters has different wavelength gain characteristics. The Peltier element is independently controlled according to the input level of the optical signal.

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